A fuel cell is a kind of a power generation device that takes out electrical energy by electrochemically oxidizing fuel such as hydrogen and methanol, and in recent years, has attracted attention as a supply source of clean energy. The fuel cell is classified into a phosphoric acid type, a molten carbonate type, a solid oxide type, a polymer electrolyte type and the like in accordance with types of electrolytes for use.
Among them, the polymer electrolyte fuel cell (PEFC) includes a membrane electrode assembly (MEA) in which electrodes are arranged on both surfaces of an electrolyte membrane. Then, the PEFC generates electricity by supplying hydrogen (fuel gas) to one surface of the membrane electrode assembly and supplying oxygen (oxidant gas) to the other surface thereof. The PEFC as described above can obtain a volumetric power density equivalent to that of an internal combustion engine, and accordingly, a research to put the PEFC into practical use as a power supply of an electric vehicle or the like is advanced (for example, refer to Patent Literatures 1 and 2).
Here, as packaging methods for the membrane electrode assembly, various types such as a stack type, a pleat type and a hollow fiber type are proposed. Among them, such a stack fuel cell is widely used, which is composed by stacking sheet-like membrane electrode assemblies on one another while separating these membrane electrode assemblies from one another by sheet-like separators.
It is catalyst layers and electrolyte membrane, each having a thickness of approximately 0.1 mm, that have a power generation function in the fuel cell. Then, for the purpose of supplying the fuel gas and the oxidant gas, which are necessary for the power generation, while efficiently removing water produced following the power generation, a typical fuel cell includes gas flow passages with a height ranging from 0.5 to 2 mm and gas diffusion layers with a height ranging from 0.2 to 0.5 mm. That is to say, a thickness (cell pitch) of a single cell of the typical fuel cell ranges from 1 to 5 mm.
Here, a standard output of the single cell of the fuel cell ranges from 0.5 to 1.5 W/cm2. Therefore, in a typical automotive fuel cell stack, a volumetric power density in an active area thereof contributing to the power generation ranges from 1 to 3 kW/L, and a volumetric power density thereof including a manifold and the like ranges from 0.5 to 1.5 kW/L.